Monday, October 21, 2019 Tickets
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Hawkins,*† Augusto H. Holmberg, L.S. Paul Johal, Jason J.
Krohn,* Emily B. Lorenz, Kenneth A. Luttrell, Vilas S.
Mujumdar, Clay J. Naito,* Clifford R. Ohlwiler, Victor F.
Pizano-Thomen, Charles L. Pizzano, Jose I. Restrepo,* Sami H.
Rizkalla, Mario E. Rodriguez,* Joseph C. Sanders,* James
Schroder, John F. Stanton, P. Jeffrey Wang, Cloyd E. Warnes,
and Michael H. Weber, Members.
*Diaphragm Subcommittee members who developed this standard.
†Diaphragm Subcommittee Chair.
Special thanks to S.K. Ghosh and S. Nakaki for their contributions to this
Abstract: ACI 550.4M prescribes testing and evaluation
requirements for mechanical connections and reinforcement at
joints intended for use under the design provisions of ASCE/
SEI 7 and ACI 318M for precast concrete diaphragms subject
to earthquake loading. These mechanical connections and
reinforcement at joints transfer the vertical and in-plane forces
between the precast concrete members that comprise the
diaphragm, and between the diaphragm and vertical elements
of the seismic-force-resisting system of the structure. The
response of precast concrete diaphragms under earthquake
loading depends not only on the strength of the connections
and the reinforcement at joints, but also on their stiffness and
deformation capacities. The seismic forces specified in ASCE/
SEI 7 for the design of precast concrete diaphragms, including
chords and collectors, in structures assigned to seismic design
category (SDC) C, D, E, or F are tied to the shear overstrength
provided by the connections and the reinforcement at joints.
This overstrength depends in turn on the design methodology,
elastic or ductile, used for the diaphragm. ACI 550.4M
prescribes the experimental procedures needed to assess the
stiffness, strength, and deformation capacity of mechanical
connections and reinforcement at joints for diaphragm
flange-to-flange connections, including chord connections, of
double-tee beams for earthquake loadings and evaluation
procedures to categorize connection performance for use with
the design procedures specified for precast concrete
diaphragms in ASCE/SEI 7 and ACI 550. ACI 550.4M does
not prescribe experimental procedures for assessing the same
information for connections for hollow-core members used in
the untopped condition.
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